ANTIOXIDANTS. ...used to prevent thermal degradation. ...inhibit oxidation (i.e. degradation) are cheap insurance for multiple pass materials

Transcription

1 ANTIOXIDANTS...used to prevent thermal degradation...inhibit oxidation (i.e. degradation) are cheap insurance for multiple pass materials Antioxidants are generally divided into primary and secondary categories. Each category has a specific function in polymer stabilization. Primary used to protect the finished product. This type of stabilization ensures performance over the life of the finished good. Typical chemistry used is phenolic-based. Secondary used as a process stabilizer. Effective way to protect the polymer during processing, especially when the polymer undergoes multiple heat histories. Typical chemistries employed include phosphites or thioesters. Primary/Secondary Combination Both primary and secondary antioxidants are often used in a combination. In this way, the polymer is protected both during the processing step and throughout its service life.

2 Effective Temperatures for Stabilizers Long Term Thermal (No Melt Processing) Hindered Amine Long Term Thermal Melt Processing Hindered Phenol Thiosyn. (&Phenol) Long Term Thermal (No Melt Processing) Phosphite Hydroxylamine Lactone Vitamin E (No Long Term Thermal) Melt Processing Temperature ( C)

3 THERMO-OXIDATIVE DEGRADATION On the molecular level, oxidation occurs in the following manner: Polymer RH R. Oxygen RO.+HO. ROO. R. + ROOH RH It is up to the antioxidant stabilizers to break the cycle and assure that the performance of the polymer is maintained. At the end of this document, references are made to specific Ampacet products that are effective in breaking the oxidation cycle.

4 NON-YELLOWING ANTIOXIDANT CONCENTRATES Phenolic discoloration can result from many conditions, including over-oxidation of hindered phenol antioxidants, pigment interaction (e.g. various grades of TiO 2 ) with phenols, cardboard yellowing, and gas fading due to the presence of NO x gases (e.g. fork lift or gas heater fumes). Two products are offered by Ampacet to help alleviate discoloration (yellowing or pinking ) which can occur with conventional phenolic antioxidant systems due to the conditions mentioned above. Products and are phenol-free and not only do not contribute to yellowing due to phenolic over-oxidation, but also help prevent discoloration when yellowing may occur from other ingredients in the polyolefin processor s formula. Both and are based in an 8 MI LDPE carrier resin (low gel, extrusion coating grade.) Product contains stearate, as the addition of stearates has been shown to lessen the formation of yellow species. For applications which cannot tolerate the addition of stearates, stearate-free should be considered. Studies performed by Ampacet have shown these phenol-free, Ampacet-proprietary mixtures are effective at minimizing or eliminating discoloration commonly associated with over-oxidation of phenolic antioxidants. Experimental work involving bot oven aging at 6 C and gas fade testing were carried out using molded low density polyethylene plaques containing 5% of a rutile grade of TiO 2 (known to aid in promoting discoloration) as a control, as well as in combination with 1 ppm of a traditional phenol/phosphite antioxidant package. 2.5% of and (yielding 1 ppm active) were then each added for determining discoloration tendencies. The attached graphs illustrate the benefits of (and 11125) over conventional phenolic-based antioxidant systems with respect to yellowing tendencies. The traditional phenolic antioxidant system is shown to actually contribute to yellowing which is illustrated by the higher yellowness index values over the control plaque which contains no antioxidant package. The addition of 2.5% or significantly decreased yellowing tendencies even in the presence of 5% of a grade of TiO 2 known to enhance discoloration.

5 Oven Aging Analysis oven aged at 6 C molded LDPE plaques with 5% uncoated TiO No Antioxidant 1 ppm Traditional Phenolic AO system 2.5% (1 ppm AO package) Time (days)

6 Gas Fade Analysis molded LDPE plaques with 5% uncoated TiO No Antioxidant 1 ppm Traditional Phenolic AO system 2.5% (1 ppm AO package) Cycles

7 AMPACET ANTIOXIDANT PRODUCTS The following list provides general information and usage guidelines for Ampacet antioxidant masterbatches. Specific antioxidants can be developed to meet special needs where required Phenol-free process stabilizer for minimal discoloration. Can also help minimize discoloration due to additives present in your letdown resin Version of with additional zinc salts for the most potent anti-coloring stabilizer properties. Should not be used where stearates are a concern Cost effective process stabilizer rich in secondary phosphite for preventing gel formation. Good for flooding extruder during down times to prevent excessive black specking upon restart Blended primary/secondary AO for high heat processes where the finished part needs good long-term outdoor life Blended phenol/phosphite for maximum outdoor durability Vitamin E masterbatch - provides outstanding melt processability (helps minimize gel formation). Best when used in combination with one of the above products. For more information, please contact Ampacet s technical support team at or Disclaimer: The information and recommendations contained in this document are based upon data collected by Ampacet and believed to be correct. However, no warranty of fitness for use or any other guarantees or warranty of any kind, expressed or implied, is made to the information contained herein, and Ampacet assumes no responsibility for the result of the use of the products and processes described herein. This is an uncontrolled document and information may be out of date.